1. Field of the Invention
The present invention relates to a process for producing an allyl ester of carboxylic acid (i.e., allyl carboxylates). More specifically, it relates to a process for producing an allyl carboxylate from a vapor phase reaction of propylene, oxygen (or oxygen-containing gas) and a lower saturated carboxylic acid.
2. Description of the Related Art
It is known in the art that allyl carboxylates are produced by the vapor phase oxidation of propylene in the presence of lower saturated carboxylic acids by using, as a catalyst, metallic palladium or palladium salts and other additives such as alkali or alkaline earth metal salts supported on a carrier. It is also known that metallic salts such as salts of gold, bismuth, iron, copper, vanadium, manganese, chromium, and molybdenium can be used as a cocatalyst in the above-mentioned vapor phase oxidation.
When the above-mentioned cocatalysts are not used, i.e., when palladium-alkali metal salt catalysts are used, the desired allyl carboxylates still can be obtained to some extent. However, since a large amount of byproducts, especially gaseous carbon dioxide, are produced, selectivity to the desired allyl carboxylates is limited. Although the amount of the carbon dioxide byproduct produced can be decreased by lowering the reaction temperature, the formation rate of the desired allyl carboxylates is thereby unpreferably decreased which is not desirable from the viewpoint of industrial production. On the other hand, when a cocatalyst such as a copper salt is used in the above-mentioned vapor phase oxidation reaction, the amount of the carbon dioxide byproducts produced is decreased. However, the formation rate of the desired allyl carboxylates is thereby unpreferably decreased, and it is believed in the art, the catalyst activity is impaired for a relatively short period of time.
Various attempts have been made to improve these disadvantages of the above-mentioned vapor phase oxidation reaction. For example, the addition of a copper salt or vanadium salt of compounds having the formula: ##STR4## wherein R.sup.4 and R.sup.5 are independently an aliphatic, aromatic, or alkoxyl group, to the reaction system has been proposed. However, although this proposed process has been found effective in the case of, for example, the salts of acetylacetone, it is not suitable as an industrial process because the use of the special agent is required.